MPP cable protection pipe and preparation method thereof

Abstract

The application belongs to the technical field of polypropylene pipe preparation, and provides MPP cable protection pipe and a preparation method thereof.The method comprises the following steps: firstly, carrying out polydopamine surface coating treatment on hexagonal boron nitride to obtain an interface heat conduction phase; secondly, melt extruding, heat stretching and heat setting of dry polyethylene terephthalate, the interface heat conduction phase and a styrene-acrylic acid glycidyl ester copolymerized oligomer to obtain a heat bridge stable shape precursor; thirdly, blending homopolymer polypropylene, copolymer polypropylene, maleic anhydride grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and an additive, and introducing the heat bridge stable shape precursor to obtain MPP pipe special material; and finally, extruding to obtain the MPP cable protection pipe.The application realizes the synergy of heat conduction interface construction, polyester microfiber stable shape and controlled compatibility of the polypropylene matrix, and takes into account the high-temperature structural stability and heat conduction capacity of the pipe.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene pipe manufacturing technology, and relates to an MPP cable protection pipe and its manufacturing method. Background Technology

[0002] MPP (modified polypropylene) cable protection pipes are widely used in power cable laying, especially in buried and trenchless construction, due to their excellent insulation, corrosion resistance, and construction adaptability. With increasing cable loads, longer operating cycles, and more enclosed and complex laying environments, the heat generated by the cable during operation is more likely to accumulate inside the protection pipe and in the adjacent pipe wall area, thus keeping the protection pipe under prolonged heating. Under these conditions, the protection pipe must not only maintain basic mechanical support and external protection functions, but also possess good high-temperature structural stability and heat conduction capacity to avoid problems such as pipe wall softening, increased deformation, and decreased service reliability caused by localized heat accumulation.

[0003] To improve the resistance to softening and deformation at high temperatures, existing MPP cable protection pipes typically employ methods such as introducing inorganic fillers, heat-resistant components, or reinforcing components to enhance the material's rigidity and thermal stability. However, while these technical approaches improve high-temperature support capabilities, they often lead to problems such as increased material density, decreased melt processing coordination, and limited interfacial heat transfer efficiency. This makes it difficult for heat generated during cable operation to be conducted and dissipated in a timely manner, hindering the reduction of localized heat accumulation. Conversely, if existing technologies focus on improving the pipe's heat conduction capacity, they may weaken the material's resistance to softening and compressive deformation under higher temperature conditions, making it difficult for the protection pipe to maintain a stable structural shape under continuous heating. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an MPP cable protection pipe and its preparation method. By constructing a polydopamine-coated hexagonal boron nitride interfacial thermally conductive phase, a thermally bridged and stable precursor material containing polyester microfiber structure is prepared and then subjected to controlled compatibility composite with a polypropylene system. Finally, an MPP cable protection pipe with both high-temperature structural stability and heat conduction capability is obtained, thereby meeting the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing an MPP cable protection tube, the method comprising:

[0007] S1, hexagonal boron nitride, Tris buffer and dopamine hydrochloride are mixed and reacted to obtain polydopamine-coated hexagonal boron nitride powder;

[0008] S2, polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder and styrene-glycidyl acrylate copolymer oligomer are mixed and added to a twin-screw extruder, and then extruded, hot-stretched and hot-set in sequence to obtain thermal bridge stabilized precursor material.

[0009] S3, homopolymer polypropylene, copolymer polypropylene, maleic anhydride grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch and thermal bridge stabilizing precursor are added to a twin-screw extruder to obtain MPP pipe material.

[0010] S4. Add the MPP pipe material to the pipe extruder and extrude to obtain the MPP cable protection pipe.

[0011] The preparation method specifically includes:

[0012] S1. Add hexagonal boron nitride to Tris buffer, then add dopamine hydrochloride, stir and react at 25-35℃ for 4-8h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 7.0-7.5. Then dry under vacuum at 70-90℃ for 6-10h to obtain polydopamine-coated hexagonal boron nitride powder.

[0013] S2, dry polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder and styrene-glycidyl acrylate copolymer oligomer are mixed and then fed into a twin-screw extruder, and extruded, hot-stretched, hot-set, cooled and pelletized in sequence to obtain thermal bridge stabilized precursor material;

[0014] S3, homopolymer polypropylene, copolymer polypropylene, maleic anhydride grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide and polypropylene masterbatch are dry-mixed to obtain a basic mixture, which is then added to a twin-screw extruder. The thermal bridge stabilizing precursor is added to the twin-screw extruder via side feeding. The mixture is melt-blended, extruded and granulated to obtain MPP pipe material.

[0015] S4. Add the MPP pipe material to the pipe extruder and extrude it to form a pipe blank. The pipe blank is then subjected to warm water sizing, cold water cooling, traction and cutting in sequence, and then heat-set at 120-140℃ for 10-25 minutes to obtain the MPP cable protection pipe.

[0016] In a weakly alkaline buffer system, the catechol groups of dopamine are first oxidized to dopaquinone, followed by intramolecular Michael addition cyclization to form cyclized dopamine. Further oxidative rearrangement yields 5,6-dihydroxyindole and its quinone oxidation products, which then polymerize stepwise through oxidative coupling and intermolecular crosslinking, depositing a polydopamine coating layer on the hexagonal boron nitride surface. The original hexagonal boron nitride surface is relatively inert. After polydopamine deposition, phenolic hydroxyl groups, amino groups, and aromatic conjugated structures are introduced onto the hexagonal boron nitride surface. The aromatic indole structure of polydopamine achieves stable adhesion to the hexagonal boron nitride basal surface through π-π stacking. Simultaneously, the phenolic hydroxyl and amino groups in polydopamine can form hydrogen bonds with the nitrogen- and oxygen-containing groups at the edges of the hexagonal boron nitride, further enhancing interfacial bonding.

[0017] In styrene-glycidyl acrylate copolymer oligomers, the epoxy groups can undergo ring-opening reactions with the terminal carboxyl and hydroxyl groups of polyethylene terephthalate (PET) to form new ester or ether bonds. The reaction between the epoxy groups and the terminal carboxyl groups of the polyester is the primary pathway, generating β-hydroxy ester bonds, leading to chain extension and localized branching of the polyester molecular chains. After chain extension, the entanglement density, melt elasticity, and tensile viscosity of the polyester melt increase. During subsequent stretching of the extruded strip, the polyester phase no longer exhibits only a fragile droplet phase but is more likely to continuously extend along the stretching direction. The polar interaction between the hydroxyl and amino groups on the surface of polydopamine-coated hexagonal boron nitride and the polyester ester groups causes hexagonal boron nitride to preferentially distribute in the polyester phase and its adjacent interfaces.

[0018] In S2, polyethylene terephthalate (PET) as the matrix is ​​combined with polydopamine-coated hexagonal boron nitride through melt extrusion, hot stretching, and heat setting. Hot stretching causes the polyester molecular chains to be highly oriented along the stretching direction, and heat setting further promotes orientation crystallization, forming a polyester-based precursor with high crystallinity and high orientation. After cooling and pelletizing, the precursor particles retain the orientation crystallization structure. In S3, the thermally bridged stabilized precursor is fed into a twin-screw extruder via side feeding. Because the processing temperature is much lower than the melting point of PET, the precursor particles do not melt in the polypropylene melt, but are gradually dispersed and stretched into a microfiber structure oriented along the flow direction under the shearing and stretching action of the screw. The orientation crystallization pre-established in S2 endows the precursor with high mechanical strength and morphological stability, making it more inclined to stretch and deform axially rather than break randomly in the shear field, thus forming polyester fibrils with a high aspect ratio. The subsequent heat setting allows the elongated polyester fibrils to maintain an independent and continuous high-melting-point skeleton morphology after heat setting. Hexagonal boron nitride sheets are oriented along the fiber axis within the polyester fibril, shortening the phonon transport path between the sheets and forming a dominant thermally conductive pathway along the fiber direction. This structure does not rely on a continuous thermally conductive network formed by the accumulation of highly filled inorganic phases throughout the entire cross-section, but rather on the directional enrichment of thermally conductive phases on the fiber skeleton and interfaces to form a heat transfer pathway under low-filling conditions.

[0019] In maleic anhydride-grafted polypropylene, the anhydride groups primarily undergo ring-opening reactions with the amine groups in the polydopamine layer on the polyester fibrils, forming amyl acid bonds (which can further dehydrate and cyclize into imide bonds at higher temperatures), thus establishing a chemical bond between the polypropylene phase and the polyester fibrils. Furthermore, the anhydride groups can also undergo esterification reactions with the phenolic hydroxyl groups in the polydopamine layer and the exposed terminal hydroxyl groups of the polyester, further enhancing interfacial bonding. Similarly, the epoxy groups in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer can undergo ring-opening reactions with the terminal carboxyl groups and hydroxyl groups of the polyester, as well as the active groups on the polydopamine surface. Its ethylene and ester segments also provide a dispersion basis within the polyolefin matrix. This allows the polypropylene melt to more fully coat the polyester fibrils, forming a transition layer at the interface with chemical bonding and intercalation characteristics.

[0020] During high-temperature service, the stress caused by localized heating can be transferred to the polyester fibrils through the interface layer. The high-melting-point oriented fibrils restrict the flow and local collapse of polypropylene segments on a macroscopic scale, thereby inhibiting the deformation expansion of the pipe wall in the heat-concentrated area. Simultaneously, hexagonal boron nitride located inside and on the surface of the polyester fibrils forms thermal bridges along the fibril direction. After heat is continuously transferred from the polypropylene to the interface layer, it can further penetrate into the thermally conductive phase-rich region and diffuse along the fibril direction. Since the thermal conductivity pathways are mainly concentrated in the fibrils and interface, rather than relying on a large amount of inorganic filler filling the entire matrix, the diffusion of localized heat is accelerated to a certain extent without significantly increasing the system density, preventing heat near the cable from remaining trapped in a limited area for extended periods.

[0021] As a preferred embodiment of the present invention, in S1, the mass ratio of hexagonal boron nitride, Tris buffer, and dopamine hydrochloride is (10-14):(180-220):(0.3-0.9), for example, it can be (10, 10.4, 10.8, 11.2, 11.6, 12, 12.4, 12.8, 13.2, 13.6 or 14):(180, 184, 188, 192, 196, 200, 204, 208, 212, 216 or 220):(0.3, 0.36, 0.42, 0.48, 0.54, 0.6, 0.66, 0.72, 0.78, 0.84 or 0.9), but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the D50 of the hexagonal boron nitride is 2-5 μm, for example, it can be 2 μm, 2.3 μm, 2.6 μm, 2.9 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.1 μm, 4.4 μm, 4.7 μm or 5 μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the concentration of the Tris buffer is 8-15 mmol / L and the pH is 8.3-8.8. For example, the concentration can be 8 mmol / L, 8.7 mmol / L, 9.4 mmol / L, 10.1 mmol / L, 10.8 mmol / L, 11.5 mmol / L, 12.2 mmol / L, 12.9 mmol / L, 13.6 mmol / L, 14.3 mmol / L, or 15 mmol / L, and the pH can be 8.3, 8.35, 8.4, 8.45, 8.5, 8.55, 8.6, 8.65, 8.7, 8.75, or 8.8, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] As a preferred embodiment of the present invention, in S2, the mass ratio of polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is (95-105):(10-14):(0.3-0.8), for example, it can be (95, 96, 97, 98, 99, 100, 101, 102, 103, 104 or 105):(10, 10.4, 10.8, 11.2, 11.6, 12, 12.4, 12.8, 13.2, 13.6 or 14):(0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.8), but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the temperatures of zones one through six of the twin-screw extruder are 245-250°C, 250-255°C, 255-260°C, 260-265°C, 263-268°C, and 265-270°C, respectively, and the die head temperature is 265-270°C. For example, the temperatures of zones one through six can be 245°C, 245.5°C, 246°C, 246.5°C, 247°C, 247.5°C, and 248°C, respectively. ℃, 248.5℃, 249℃, 249.5℃ or 250℃), (250℃, 250.5℃, 251℃, 251.5℃, 252℃, 252.5℃, 253℃, 253.5℃, 254℃, 254.5℃ or 255℃), (255℃, 255.5℃, 256℃, 256.5℃, 257℃, 257.5℃, 258℃, 258.5℃, 259℃, 259.5℃ or 2 (60℃), (260℃, 260.5℃, 261℃, 261.5℃, 262℃, 262.5℃, 263℃, 263.5℃, 264℃, 264.5℃ or 265℃), (263℃, 263.5℃, 264℃, 264.5℃, 265℃, 265.5℃, 266℃, 266.5℃, 267℃, 267.5℃ or 268℃), (265℃, 265.5℃, 266℃) The machine head temperature can be 265℃, 265.5℃, 266℃, 266.5℃, 267℃, 268℃, 268.5℃, 269℃, 269.5℃ or 270℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the hot stretching involves melt extruding the material into strips, cooling them to room temperature in a water bath, and then stretching them 4-8 times using hot stretching rollers at 85-115°C. For example, the temperature of the hot stretching rollers can be 85°C, 88°C, 91°C, 94°C, 97°C, 100°C, 103°C, 106°C, 109°C, 112°C, or 115°C, and the stretching ratio can be 4 times, 4.4 times, 4.8 times, 5.2 times, 5.6 times, 6 times, 6.4 times, 6.8 times, 7.2 times, 7.6 times, or 8 times, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the heat setting is performed at 170-200°C for 20-90 seconds. For example, the heat setting temperature can be 170°C, 173°C, 176°C, 179°C, 182°C, 185°C, 188°C, 191°C, 194°C, 197°C, or 200°C, and the heat setting time can be 20 seconds, 27 seconds, 34 seconds, 41 seconds, 48 ​​seconds, 55 seconds, 62 seconds, 69 seconds, 76 seconds, 83 seconds, or 90 seconds, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] As a preferred embodiment of the present invention, in S3, the mass ratio of homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene masterbatch, and thermal bridge stabilizing precursor is (58-66):(20-24):(1.2-2.2):(0.5-1):(0.08-0.12):(0.08-0.12):(0.08-0.15):(0.2-0.4):(0. 2-0.5): (10-14), for example, it could be (58, 58.8, 59.6, 60.4, 61.2, 62, 62.8, 63.6, 64.4, 65.2 or 66): (20, 20.4, 20.8, 21.2, 21.6, 22, 22.4, 22.8, 23.2, 23.6 or 24): (1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1 or 2.2): (0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0. 85, 0.9, 0.95 or 1): (0.08, 0.084, 0.088, 0.092, 0.096, 0.1, 0.104, 0.108, 0.112, 0.116 or 0.12): (0.08, 0.084, 0.088, 0.092, 0.096, 0.1, 0.104, 0.108, 0.112, 0.116 or 0.12): (0.08, 0.087, 0.094, 0.101, 0.108, 0.115, 0.122, 0.129, 0.136, 0.1 43 or 0.15): (0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38 or 0.4): (0.2, 0.23, 0.26, 0.29, 0.32, 0.35, 0.38, 0.41, 0.44, 0.47 or 0.5): (10, 10.4, 10.8, 11.2, 11.6, 12, 12.4, 12.8, 13.2, 13.6 or 14), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0029] In some optional embodiments, the temperatures of zones one to six of the twin-screw extruder are 175-185℃, 180-190℃, 185-195℃, 190-200℃, 195-205℃, and 195-205℃, respectively, and the die head temperature is 200-210℃. For example, the temperatures of zones one to six can be 175℃, 176℃, 177℃, 178℃, ... 9℃, 180℃, 181℃, 182℃, 183℃, 184℃ or 185℃), (180℃, 181℃, 182℃, 183℃, 184℃, 185℃, 186℃, 187℃, 188℃, 189℃ or 190℃), (185℃, 186℃, 187℃, 188℃, 189℃, 190℃, 191℃, 192℃, 193℃, 1 94℃ or 195℃), (190℃, 191℃, 192℃, 193℃, 194℃, 195℃, 196℃, 197℃, 198℃, 199℃ or 200℃), (195℃, 196℃, 197℃, 198℃, 199℃, 200℃, 201℃, 202℃, 203℃, 204℃ or 205℃), (195℃, 196℃, 197℃) The head temperature can be 200℃, 201℃, 202℃, 203℃, 204℃ or 205℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] As a preferred embodiment of the present invention, in S4, the temperatures of zones one to three of the pipe extruder are 185-195℃, 190-200℃, and 195-205℃, respectively; the temperature of the connecting section is 200-210℃; and the temperature of the die head and die is 205-220℃. For example, the temperatures of zones one to three can be (185℃, 186℃, 187℃, 188℃, 189℃, 190℃, 191℃, 192℃, 193℃, 194℃, or 195℃), (190℃, 191℃, 192℃, 193℃, 194℃, 195℃, 196℃, 197℃, 198℃, 199℃, or 200℃), and (…). The temperatures of the connecting sections can be 200℃, 201℃, 202℃, 203℃, 204℃, or 205℃, and the temperatures of the die head and die can be 205℃, 206.5℃, 208℃, 209.5℃, 211℃, 212.5℃, 214℃, 215.5℃, 217℃, 218.5℃, or 220℃, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] Secondly, the present invention provides an MPP cable protection tube prepared by the preparation method described in the first aspect.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: By constructing a polydopamine interface layer on the surface of hexagonal boron nitride, the present invention transforms the thermally conductive phase from a low interfacial affinity state into a functional phase that can have a stable interfacial interaction with the polyester phase and the polypropylene compatibility system, which is beneficial to reducing the dispersion resistance of fillers and the interfacial heat transfer resistance in the organic matrix; by introducing the interfacial thermally conductive phase into the polyethylene terephthalate precursor system, the polyester phase is transformed from a common dispersed phase into an oriented microfiber skeleton that can be retained in subsequent processing and can constrain the local thermal softening and compressive deformation of the polypropylene continuous phase after tube formation, while providing a continuous distribution path for the thermally conductive phase; furthermore, maleic anhydride-grafted polypropylene and epoxy-containing compatibility components work together on the interface between the polypropylene continuous phase and the polyester microfiber, enhancing the interfacial bonding without destroying the independent morphology of the polyester microfiber, so that heat and load can be effectively transferred between the continuous phase, the interface layer and the microfiber skeleton; thus, the present invention can reduce local heat accumulation and maintain the structural stability and service reliability of the pipe under high temperature conditions without relying on high filler thermally conductive components. Attached Figure Description

[0033] Figure 1 This is a SEM image of the polydopamine-coated hexagonal boron nitride powder provided in Example 1 of the present invention. Detailed Implementation

[0034] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0035] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0036] Example 1

[0037] This embodiment provides an MPP cable protection pipe and its preparation method, the preparation method specifically includes the following steps:

[0038] S1, add hexagonal boron nitride with a D50 of 2 μm to Tris buffer solution with a concentration of 15 mmol / L and a pH of 8.3, and then add dopamine hydrochloride. The mass ratio of hexagonal boron nitride, Tris buffer solution and dopamine hydrochloride is 10:220:0.3. Stir and react at 25 °C for 8 h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 7.0. Then vacuum dry at 90 °C for 6 h to obtain polydopamine-coated hexagonal boron nitride powder.

[0039] S2, dried polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and a styrene-glycidyl acrylate copolymer oligomer with a weight-average molecular weight of 6800, an epoxy equivalent of 280 g / eq, and a glass transition temperature of 54°C are mixed and fed into a twin-screw extruder. The mass ratio of the polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is 95:14:0. 8. The temperatures of zones one to six of the twin-screw extruder are 250°C, 250°C, 260°C, 260°C, 268°C, and 265°C, respectively, and the die head temperature is 270°C. The extrusion, hot stretching, hot setting, cooling and pelletizing are performed sequentially. The hot stretching is performed by melt extrusion into strips, followed by water bath cooling to room temperature, and then 8 times stretching through 85°C hot stretching rollers. The hot setting is performed by hot setting at 200°C for 20 seconds to obtain the thermal bridge stabilized precursor material.

[0040] S3, a basic mixture is prepared by dry mixing homopolymer polypropylene with a melt index of 0.3 g / 10 min (230℃ / 2.16 kg), copolymer polypropylene with a melt index of 0.6 g / 10 min, maleic anhydride grafted polypropylene with a grafting rate of 0.8 wt.% and a melt index of 80 g / 10 min, ethylene-methyl acrylate-glycidyl methacrylate terpolymer with a melt index of 4 g / 10 min and a melting point of 60℃, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, and polypropylene masterbatch. The thermal bridge stabilizing precursor is then added to a twin-screw extruder via side feeding. The homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch, and thermal bridge stabilizing precursor are mixed in a mass ratio of 66:20:1.2:1:0.08:0.12:0.08:0.4:0.2:14. The temperatures of zones one to six of the twin-screw extruder are 175℃, 190℃, 185℃, 200℃, 195℃, and 205℃, respectively, and the die head temperature is 200℃. The mixture is melt-blended, extruded, and granulated to obtain MPP pipe material.

[0041] S4. MPP pipe material is added to the pipe extruder. The temperatures of the first to third zones of the pipe extruder are 195°C, 190°C and 205°C, respectively. The temperature of the connecting section is 210°C, and the temperature of the die head and die is 205°C. The extrusion forms a pipe blank. The pipe blank is then sized in 46°C warm water for 75s, cooled in 23°C cold water for 90s, drawn and cut at 2.2m / min, and then heat-set at 120°C for 25min to obtain the MPP cable protection pipe.

[0042] Figure 1 The image shows a SEM image of the polydopamine-coated hexagonal boron nitride powder provided in this embodiment, with obvious polydopamine deposition on the surface of the sheets.

[0043] Example 2

[0044] This embodiment provides an MPP cable protection pipe and its preparation method, the preparation method specifically includes the following steps:

[0045] S1, add hexagonal boron nitride with a D50 of 5 μm to Tris buffer solution with a concentration of 8 mmol / L and a pH of 8.8, and then add dopamine hydrochloride. The mass ratio of hexagonal boron nitride, Tris buffer solution and dopamine hydrochloride is 14:180:0.9. Stir and react at 35 °C for 4 h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 7.5. Then vacuum dry at 70 °C for 10 h to obtain polydopamine-coated hexagonal boron nitride powder.

[0046] S2, dry polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and an epoxy equivalent of 320 with a weight average molecular weight of 7500 are combined. A styrene-glycidyl acrylate copolymer oligomer with a glass transition temperature of 60°C and g / eq is mixed and fed into a twin-screw extruder. The mass ratio of polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is 105:10:0.3. The temperatures of zones one to six of the twin-screw extruder are 245°C, 255°C, 255°C, 265°C, 263°C, and 270°C, respectively, and the die head temperature is 265°C. The extrusion, hot stretching, heat setting, cooling, and pelletizing are performed sequentially. The hot stretching is performed by melt extrusion into strips, followed by water bath cooling to room temperature, and then 4 times stretching through a 115°C hot stretching roller. The heat setting is performed at 170°C for 90 seconds to obtain a thermal bridge-stabilized precursor material.

[0047] S3, a basic mixture is prepared by dry mixing homopolymer polypropylene with a melt index of 0.8 g / 10 min (230℃ / 2.16 kg), copolymer polypropylene with a melt index of 1.3 g / 10 min, maleic anhydride grafted polypropylene with a grafting rate of 1.2 wt.% and a melt index of 130 g / 10 min, ethylene-methyl acrylate-glycidyl methacrylate terpolymer with a melt index of 8 g / 10 min and a melting point of 70℃, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, and polypropylene masterbatch. The thermal bridge stabilizing precursor is then added. The material is fed into a twin-screw extruder via side feeding. The mass ratio of homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene masterbatch, and thermal bridge stabilizing precursor is 58:24:2.2:0.5:0.12:0.08:0.15:0.2:0.5:10. The temperatures of zones one to six of the twin-screw extruder are 185℃, 180℃, 195℃, 190℃, 205℃, and 195℃, respectively, and the die head temperature is 210℃. The mixture is melt-blended, extruded, and granulated to obtain MPP pipe-specific material.

[0048] S4. MPP pipe material is added to the pipe extruder. The temperatures of the first to third zones of the pipe extruder are 185°C, 200°C and 195°C, respectively. The temperature of the connecting section is 200°C, and the temperature of the die head and die is 220°C. The extrusion forms a pipe blank. The pipe blank is then sized in 55°C warm water for 50s, cooled in 18°C ​​cold water for 180s, and cut at a speed of 1.0m / min. Finally, it is heat-set at 140°C for 10min to obtain the MPP cable protection pipe.

[0049] Example 3

[0050] This embodiment provides an MPP cable protection pipe and its preparation method, the preparation method specifically includes the following steps:

[0051] S1, add hexagonal boron nitride with a D50 of 3 μm to Tris buffer solution with a concentration of 10 mmol / L and a pH of 8.5, and then add dopamine hydrochloride. The mass ratio of hexagonal boron nitride, Tris buffer solution and dopamine hydrochloride is 11:200:0.5. Stir and react at 30°C for 6 h. After the reaction is completed, filter and wash with deionized water until the pH of the filtrate is 7.2. Then vacuum dry at 80°C for 8 h to obtain polydopamine-coated hexagonal boron nitride powder.

[0052] S2, dry polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and an epoxy equivalent of 290 with a weight average molecular weight of 7000 are combined. A styrene-glycidyl acrylate copolymer oligomer with a glass transition temperature of 56°C and g / eq is mixed and fed into a twin-screw extruder. The mass ratio of polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is 100:12:0.5. The temperatures of zones one to six of the twin-screw extruder are 248°C, 252°C, 258°C, 262°C, 265°C, and 268°C, respectively, and the die head temperature is 268°C. The extrusion, hot stretching, heat setting, cooling, and pelletizing are performed sequentially. The hot stretching is performed by melt extrusion into strips, followed by water bath cooling to room temperature, and then 6 times stretching through a 100°C hot stretching roller. The heat setting is performed at 185°C for 50 seconds to obtain a thermal bridge-stabilized precursor material.

[0053] S3, a basic mixture is prepared by dry mixing homopolymer polypropylene with a melt index of 0.5 g / 10 min (230℃ / 2.16 kg), copolymer polypropylene with a melt index of 0.8 g / 10 min, maleic anhydride grafted polypropylene with a grafting rate of 0.9 wt.% and a melt index of 90 g / 10 min, ethylene-methyl acrylate-glycidyl methacrylate terpolymer with a melt index of 5 g / 10 min and a melting point of 63℃, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, and polypropylene masterbatch. The thermal bridge stabilizing precursor is then fed into a twin-screw extruder via side feeding. The homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch, and thermal bridge stabilizing precursor are in a mass ratio of 60:22:1.5:0.8:0.10:0.10:0.10:0.3:0.3:12. The temperatures of the first to sixth zones of the twin-screw extruder are 180℃, 185℃, 190℃, 195℃, 200℃, and 200℃, respectively, and the die head temperature is 205℃. The mixture is melt-blended, extruded, and granulated to obtain MPP pipe-specific material.

[0054] S4. MPP pipe material is added to the pipe extruder. The temperatures of the first to third zones of the pipe extruder are 190°C, 195°C and 200°C, respectively. The temperature of the connecting section is 205°C, and the temperature of the die head and die is 210°C. The extrusion forms a pipe blank. The pipe blank is then sized in 40°C warm water for 90s, cooled in 25°C cold water for 120s, and cut at a speed of 1.6m / min. Finally, it is heat-set at 130°C for 15min to obtain the MPP cable protection pipe.

[0055] Example 4

[0056] This embodiment provides an MPP cable protection pipe and its preparation method, the preparation method specifically includes the following steps:

[0057] S1, hexagonal boron nitride with a D50 of 4 μm was added to a Tris buffer solution with a concentration of 12 mmol / L and a pH of 8.6, and then dopamine hydrochloride was added. The mass ratio of hexagonal boron nitride, Tris buffer solution and dopamine hydrochloride was 13:190:0.7. The mixture was stirred at 28 °C for 5 h. After the reaction was completed, the mixture was filtered and washed with deionized water until the pH of the filtrate was 7.4. The filtrate was then vacuum dried at 85 °C for 7 h to obtain polydopamine-coated hexagonal boron nitride powder.

[0058] S2, dry polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and an epoxy equivalent of 300 were mixed. A styrene-glycidyl acrylate copolymer oligomer with a glass transition temperature of 58°C and g / eq is mixed and fed into a twin-screw extruder. The mass ratio of polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is 102:11:0.6. The temperatures of zones one to six of the twin-screw extruder are 247°C, 253°C, 257°C, 263°C, 266°C, and 269°C, respectively, and the die head temperature is 267°C. The extrusion, hot stretching, and heat setting are performed sequentially, followed by cooling and pelletizing. The hot stretching involves melt extrusion into strips, followed by water bath cooling to room temperature, and then 5 times stretching through a 105°C hot stretching roller. The heat setting is performed at 190°C for 70 seconds to obtain a thermally bridged stabilizing precursor material.

[0059] S3, a basic mixture is prepared by dry mixing homopolymer polypropylene with a melt index of 0.6 g / 10 min (230℃ / 2.16 kg), copolymer polypropylene with a melt index of 1.0 g / 10 min, maleic anhydride grafted polypropylene with a grafting rate of 1.1 wt.% and a melt index of 120 g / 10 min, ethylene-methyl acrylate-glycidyl methacrylate terpolymer with a melt index of 7 g / 10 min and a melting point of 68℃, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, and polypropylene masterbatch. The thermal bridge stabilizing precursor is then fed into a twin-screw extruder via side feeding. The homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch, and thermal bridge stabilizing precursor have a mass ratio of 64:23:2.0:0.7:0.11:0.11:0.12:0.25:0.4:11. The temperatures of zones one to six of the twin-screw extruder are 182℃, 188℃, 192℃, 198℃, 202℃, and 202℃, respectively, and the die head temperature is 208℃. The mixture is melt-blended, extruded, and granulated to obtain MPP pipe-specific material.

[0060] S4, MPP pipe material is added to the pipe extruder. The temperatures of the first to third zones of the pipe extruder are 192°C, 198°C and 202°C, respectively. The temperature of the connecting section is 208°C, and the temperature of the die head and die is 215°C. The extrusion forms a pipe blank. The pipe blank is then sized in 51°C warm water for 30s, cooled in 15°C cold water for 60s, and cut at a speed of 3.0m / min. Finally, it is heat-set at 135°C for 20min to obtain the MPP cable protection pipe.

[0061] Comparative Example 1

[0062] This comparative example provides an MPP cable protection pipe and its preparation method. The difference between this example and Example 1 is that hot stretching and heat setting are not performed in S2, while other process parameters and operating conditions are exactly the same as in Example 1.

[0063] Comparative Example 2

[0064] This comparative example provides an MPP cable protection pipe and its preparation method. The difference between this example and Example 1 is that no thermal bridge stabilizing precursor is added in S3, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0065] Performance testing:

[0066] The Vicat softening temperature test method refers to DL / T 802.7-2023;

[0067] The density test method refers to GB / T 1033.1-2008;

[0068] Simulated current-carrying heat dissipation test method: An MPP cable protection tube sample with an outer diameter of 50 mm and a length of 1000 mm was used. An electric heating rod with an outer diameter of 10 mm and an effective heating length of 600 mm was placed at the center of the tube along its axis and fixed with a PTFE insulating support, ensuring a coaxial distance between the outer surface of the heating rod and the inner wall of the tube. Both ends of the protection tube were semi-closed with heat-resistant insulating plugs, leaving only the wire lead-out holes. The sample was placed at 23±2℃, relative humidity 50±10%, and without forced draft for 24 hours before testing. During testing, a constant power DC power supply continuously input 100W of power to the electric heating rod. K-type thermocouples were used to measure the surface temperature of the electric heating rod, the temperature at the middle of the inner wall of the tube, the temperature at the middle of the outer wall of the tube, and the ambient temperature 20 mm from the outer wall of the tube, with a temperature acquisition interval of 10 seconds. Power was continuously supplied until the surface temperature change of the electric heating rod did not exceed 1.0℃ for 30 consecutive minutes, at which point a steady state was considered reached. Record the surface temperature of the electric heating rod, the inner wall temperature of the tube, the outer wall temperature of the tube, and the ambient temperature at steady state, and calculate the steady-state temperature rise of the electric heating rod ΔT1=T. 加热棒 -T 环境 The steady-state temperature difference between the inner and outer surfaces of the pipe wall is ΔT2=T 内壁 -T 外壁 The smaller ΔT1 and ΔT2 are, the better the heat dissipation performance of the protective tube.

[0069] The test results are shown in Table 1.

[0070] Table 1. Test results of MPP cable protection pipes prepared in Examples 1-4 and Comparative Examples 1-2

[0071] Vicat softening temperature (°C) <![CDATA[Density (g / cm 3 )]]> <![CDATA[ΔT1(℃)]]> <![CDATA[ΔT2(℃)]]> Example 1 148 0.98 64.8 5.3 Example 2 145 0.97 65.4 5.5 Example 3 147 0.98 64.1 5.1 Example 4 149 0.99 65.0 5.4 Comparative Example 1 139 0.98 69.2 8.9 Comparative Example 2 136 0.96 74.6 12.7

[0072] As shown in Table 1, compared to Example 1, the Vicat softening temperature and heat dissipation performance of Comparative Example 1 and Comparative Example 2 are both lower. This is because, in Comparative Example 1, without hot stretching and heat setting, the polyester phase mainly exists in a common dispersed state, making it difficult to form and retain a continuous fibrillary skeleton. The directional enrichment of hexagonal boron nitride along the fibrils and interfaces is weakened, the local heat diffusion path is shortened, and the structural constraint on the continuous polypropylene phase when heated is weakened. Therefore, the Vicat softening temperature decreases, and the heat dissipation capacity decreases. In Comparative Example 2, without the addition of thermal bridge stabilizing precursors, the system only contains a common polypropylene matrix and conventional compatible components. It lacks the restriction of the thermal softening zone by the high-melting-point polyester microfiber skeleton and also lacks the thermal bridge pathway formed by hexagonal boron nitride and the interface layer. Heat is more likely to accumulate locally, increasing the heat transfer resistance of the pipe wall.

[0073] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an MPP cable protection pipe, characterized in that, The preparation method includes: S1, hexagonal boron nitride, Tris buffer and dopamine hydrochloride are mixed and reacted to obtain polydopamine-coated hexagonal boron nitride powder; S2, polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder and styrene-glycidyl acrylate copolymer oligomer are mixed and added to a twin-screw extruder, and then extruded, hot-stretched and hot-set in sequence to obtain thermal bridge stabilized precursor material. S3, homopolymer polypropylene, copolymer polypropylene, maleic anhydride grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch and thermal bridge stabilizing precursor are added to a twin-screw extruder to obtain MPP pipe material. S4, add the MPP pipe material to the pipe extruder and extrude to obtain the MPP cable protection pipe; The mass ratio of hexagonal boron nitride, Tris buffer, and dopamine hydrochloride is (10-14):(180-220):(0.3-0.9). The mass ratio of polyethylene terephthalate, polydopamine-coated hexagonal boron nitride powder, and styrene-glycidyl acrylate copolymer oligomer is (95-105):(10-14):(0.3-0.8). The mass ratio of homopolymer polypropylene, copolymer polypropylene, maleic anhydride-grafted polypropylene, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, antioxidant 1010, antioxidant 168, calcium stearate, ethylene bis-stearamide, polypropylene color masterbatch and thermal bridge stabilizing precursor is (58-66):(20-24):(1.2-2.2):(0.5-1):(0.08-0.12):(0.08-0.12):(0.08-0.15):(0.2-0.4):(0.2-0.5):(10-14).

2. The method for preparing an MPP cable protection pipe according to claim 1, characterized in that, In S1: The concentration of the Tris buffer solution is 8-15 mmol / L and the pH is 8.3-8.

8.

3. The method for preparing an MPP cable protection pipe according to claim 1, characterized in that, In S2: The temperatures of the first to sixth zones of the twin-screw extruder are 245-250℃, 250-255℃, 255-260℃, 260-265℃, 263-268℃, and 265-270℃, respectively, and the die head temperature is 265-270℃.

4. The method for preparing an MPP cable protection pipe according to claim 1, characterized in that, In S2: The hot stretching process involves melt extrusion into strips, followed by water bath cooling to room temperature, and then stretching by 4-8 times using hot stretching rollers at 85-115℃. The heat setting is performed at 170-200℃ for 20-90 seconds.

5. The method for preparing an MPP cable protection pipe according to claim 1, characterized in that, In S3: The temperatures of the first to sixth zones of the twin-screw extruder are 175-185℃, 180-190℃, 185-195℃, 190-200℃, 195-205℃, and 195-205℃, respectively, and the die head temperature is 200-210℃.

6. The method for preparing an MPP cable protection pipe according to claim 1, characterized in that, In S4: The temperatures of the first to third zones of the pipe extruder are 185-195℃, 190-200℃ and 195-205℃, respectively; the temperature of the connecting section is 200-210℃; and the temperature of the die head and die is 205-220℃.

7. An MPP cable protection pipe, characterized in that, It is obtained by the preparation method according to any one of claims 1-6.

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